I scrolled through the feature requests but I couldn’t finde something similar.
What I mean with working time:
I work for a customer and record only my work and time i spent.
So the system has to record “what I worked, when I worked” and mark it to that customer.
After a self defined time period I issue a bill for him.
On it its written every single work, the time is needed on every support and of course a total price.
An extension could be Packaged Working Time:
I sell to a customer a 10 hour package and from that package my working time is reduced.
All the time I can tell the customer how much support time is left, and can sell a new package.
It should be able to issue a monthly report where is written, which kind of package he bought, what I worked and how much is left from that package.
I hope I could explain it more or less confusing free, but of course if there are any question, I am happy to discuss.
To show my seriousness I would donate for that feature 100 Euro.